Reactor with gas distribution system in bottom

ABSTRACT

The invention relates to a reactor for carrying out an exothermic process comprising a reactor shell, inlets for introducing reactants and coolant into the reactor shell, outlets for removing product and coolant from the reactor shell, at least two reactor tubes, a coolant chamber, and a gas distribution system below the coolant chamber, whereby at least two reactor tubes extend through the coolant chamber to enable fluid communication between the space below the coolant chamber and the space above the coolant chamber, said reactor comprising one or more highly porous catalysts, said catalyst(s) having a size of at least 1 mm and comprising a porous body and a catalyst material, whereby the porous body has a porosity within the range of between 50 and 98 volume %.

This application claims the benefit of European Application No.09180825.3 filed Dec. 28, 2009, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a reactor for carrying out anexothermic process, such as a Fischer-Tropsch process. It especiallyrelates to a fixed bed reactor comprising a gas distribution system inthe bottom of the reactor. In a preferred embodiment the reactorcomprises highly porous catalysts. The invention further relates to theuse of the reactor.

As is explained in WO 2005/075065, Fischer-Tropsch processes are oftenused for the conversion of gaseous hydrocarbon feed stocks into liquidand/or solid hydrocarbons. The feed stock, e.g. natural gas, associatedgas, coal-bed methane, residual (crude) oil fractions, coal and/orbiomass is converted in a first step to a mixture of hydrogen and carbonmonoxide, also known as synthesis gas or syngas. The synthesis gas isthen converted in a second step over a suitable catalyst at elevatedtemperature and pressure into paraffinic compounds ranging from methaneto high molecular weight molecules comprising up to 200 carbon atoms,or, under particular circumstances, more.

Numerous types of reactor systems have been developed for carrying outthe Fischer-Tropsch reaction. Fischer-Tropsch reactor systems includefixed bed reactors, in particular multi-tubular fixed bed reactors,fluidized bed reactors, such as entrained fluidized bed reactors andfixed fluidized bed reactors, and slurry bed reactors, such asthree-phase slurry bubble columns and ebullated bed reactors.

The Fischer-Tropsch reaction is highly exothermic and temperaturesensitive and thus requires careful temperature control to maintainoptimum operating conditions and hydrocarbon product selectivity.

Commercial Fischer Tropsch fixed-bed and three-phase slurry reactorstypically utilize boiling water to remove reaction heat. In fixed-bedreactors, individual reactor tubes are located within a shell containingwater/steam typically fed to the reactor via flanges in the shell wall.The reaction heat raises the temperature of the catalyst bed within eachtube. This thermal energy is transferred to the tube wall forcing thesurrounding water to boil. In the slurry design, cooling tubes areplaced within the slurry volume and heat is transferred from the liquidcontinuous matrix to the tube walls. The production of steam within thetubes provides cooling.

SUMMARY OF THE INVENTION

The present invention provides an improved reactor for carrying out anexothermic process, such as a Fischer-Tropsch process.

The present invention concerns a reactor (1) for carrying out anexothermic process, comprising a reactor shell (2), inlets (3, 7) forintroducing reactants and coolant into the reactor shell (2), outlets(4, 8) for removing product and coolant from the reactor shell (2), atleast two reactor tubes (9), a coolant chamber (6), and a gasdistribution system (11) below the coolant chamber (6), whereby at leasttwo reactor tubes (9) extend through the coolant chamber (6) to enablefluid communication between the space (15) below the coolant chamber (6)and the space (13) above the coolant chamber (6), said reactor (1)comprising one or more highly porous catalysts. The catalyst(s) have asize of at least 1 mm. The catalyst(s) comprise(s) a porous body and acatalyst material. The porous body has a porosity within the range ofbetween 50 and 98 volume %.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a vertical cross-section of a reactor according to the presentinvention; the catalyst in the reactor tubes is not shown.

DETAILED DESCRIPTION OF THE INVENTION

Catalysts having a size of at least 1 mm are defined as catalysts havinga longest internal straight length of at least 1 mm. Preferably, thehighly porous catalyst has pores with a size of more than 10 μm. Thecatalyst material comprises a carrier and a catalytically activecomponent or precursor therefor. A precursor of a catalytically activecomponent can be made catalytically active by subjecting it to hydrogenor a hydrogen containing gas.

A reactor according to the present invention has several advantages. Oneadvantage of a reactor according to the present invention is that it ispossible to have a very good heat transfer between the catalyst and thecooling medium in the coolant chamber as compared to the heat transferbetween the catalyst and the cooling medium in a fixed bed reactorcomprising a packing of solid catalyst particles. The heat transfer in areactor according to the present invention is also better as compared toa multi-tubular fixed bed reactor comprising a highly porous catalyst inthe reactor tubes, wherein the reactant gases flow from the top of thereactor tubes downwards through the reactor tubes.

Good heat transfer allows using larger tube diameters, and thus lesstubes per reactor volume. This makes the reactor simpler to build and tooperate.

Another advantage of a reactor according to the present invention isthat a low pressure drop along the reactor tube can be obtained ascompared to a fixed bed reactor comprising a packing of solid catalystparticles. A low pressure drop reduces the costs and the energyconsumption of feed gas and/or recycle gas compressor(s).

A further advantage of a reactor according to the present invention isthat up-scaling can be performed more easily and more reliably ascompared to slurry reactors comprising fluidized catalyst particles.This is because the design of a commercial reactor can rely on smallscale testing of a single tube. Up-scaling can simply and reliably beperformed by multiplication of the number of reactor tubes.

Another advantage of a reactor according to the present invention isthat a uniform distribution of catalyst within the reactor can beobtained, independent of hydrodynamic operating conditions. Evenstacking of different catalyst structures within a single reactor tubecan be applied. This is a big advantage over slurry reactors comprisinga vessel or shell with a plurality of coolant tubes. Preferably a highlyporous catalyst as described below, or a stacking or gradient ofdifferent highly porous catalysts as described below, is applied.

A further advantage of a reactor according to the present invention isthat the product can be easily separated from the catalyst. This is abig advantage over slurry reactors comprising fluidized catalystparticles.

The coolant chamber (6) preferably comprises at least two substantiallyparallel plates (16, 17) which separate the coolant chamber (6) from thespace (15) below the coolant chamber (6) and the space (13) above thecoolant chamber (6). Such substantially parallel plates (16, 17)preferably are substantially horizontal. Preferably at least two reactortubes (9) that extend through the coolant chamber (6) also extendthrough the at least substantially parallel plates (16, 17) of thecoolant chamber (6).

The reactor preferably comprises less than 50000 reactor tubes, morepreferably less than 30000, even more preferably less than 10000, mostpreferably less than 5000. The reactor preferably comprises at least 10reactor tubes, more preferably at least 100, even more preferably atleast 1000, most preferably at least 2000.

The reactor tubes preferably have a length of more than 1 meter, morepreferably more than 5 meters, even more preferably more than 7 meters.The reactor tubes preferably have a length of less than 70 meters, morepreferably less than 40 meters, even more preferably less than 20meters.

The reactor tubes preferably have an inner diameter of at least 1 cm,more preferably at least 2 cm, even more preferably at least 5 cm. Thereactor tubes preferably have an inner diameter of less than 30 cm, morepreferably less than 20 cm, even more preferably less than 15 cm.

Preferably at least 70%, more preferably at least 80% of each reactortube is in the coolant chamber.

The inlet(s) for introducing coolant into the reactor shell and theoutlet(s) for removing coolant from the reactor shell are preferablybetween the parallel plates that separate the coolant chamber from thespace below and the space above the coolant chamber. More preferably,one or more coolant inlets are placed just above the lowest parallelplate of the coolant chamber, and one or more coolant outlets are placedjust below the highest parallel plate of the coolant chamber.

The inlet(s) for introducing reactants into the reactor shell preferablyare below the coolant chamber. One or more inlets for introducingreactants may be situated through substantially vertical reactor shellbelow the coolant chamber and/or may be situated through the dome at thebottom of the reactor. An inlet for introducing reactants preferablycomprises a nozzle.

The reactant gas is preferably distributed and supplied to individualreactor tubes. The gas distribution system 11 preferably passes gas fromthe inlet 3 to reactor tubes 9 via distribution system outlets that areplaced in and/or underneath the reactor tubes. The reactant gas, forexample syngas, flows upwards through the catalysts in the reactor tubesand is converted into products. Generally not all syngas that passesthrough a catalyst is converted into products.

In one embodiment, the gas distribution system comprises a substantiallyhorizontal piping that is installed below the tubes, e.g. in rows. Thepipes have several reactant gas outlets. The pipes may, for example, beperforated. Additionally or alternatively, the pipes may, for example,have small pipes in a vertical direction that guides the gas into theindividual tubes. In a preferred embodiment the small pipes extend intothe lower part of the tubes.

In order to have a minimal number of reactant gas inlets through thereactor shell, one embodiment comprises a gas distribution system withrows of pipes comprising reactant gas outlets, and whereby the rows ofpipes are connected to larger distribution piping. The largerdistribution piping may, for example, be in the form of a ring.

In a preferred embodiment, the gas distribution system is designed suchthat every reactor tube that is supplied with reactant gas receives asimilar amount of reactant gas. This assures even conversion throughoutthe reactor. This also contributes to a good heat transfer both by evenconversion and by even liquid movement in the reactor.

The outlet(s) for removing product may be above and/or below the coolantchamber. The outlet(s) for removing product may additionally oralternatively be at the level of the coolant chamber. An outlet abovethe coolant chamber may, for example, comprise an overflow weir. Liquiddraw-off through an outlet below the coolant chamber may, for example,be based on level control. In case of level control, the level of liquidproduct in the reactor provides a set-point for draw-off via a flowcontroller. Preferably the reactor comprises an outlet below the coolantchamber. When product is removed below the coolant chamber no or almostno gas will be dragged with the liquid product. Product removed belowthe coolant chamber will thus probably contain less gaseous products,e.g. H₂O, C₄-products, CO₂, CO and H₂, as compared to product removedabove the coolant chamber. An outlet below the coolant chamber alsoprovides the possibility to empty the reactor

Most preferably the discharge of product is on basis of level control.For example, a level control with a range of several meters may beplaced above the coolant chamber to regulate a valve in an outlet forremoving product below the coolant chamber. In that case liquid productis discharged via the outlet below the coolant chamber on basis of thelevel control above the coolant chamber.

In a preferred embodiment, during use of the reactor according to theinvention, the amount of liquid in the reactor is sufficiently large tohave the catalyst in the reactor tubes immersed in liquid, even when noreactant gas is flowing into the reactor. This may be adjusted by meansof level control.

During use of the reactor according to the invention, there is gasupflow, or co-current upflow of gas and liquid.

In a preferred embodiment, the reactor comprises reactor tubes as wellas one or more liquid recycle tubes. The reactor tubes contain catalystduring use of the reactor. Liquid recycle tubes are tubes which do notcontain catalyst during use of the reactor. A liquid recycle tube (18)may extend through the coolant chamber (6) to enable fluid communicationbetween the space (15) below the coolant chamber (6) and the space (13)above the coolant chamber (6). During use, liquid is transferred upwardsin the reactor tubes (9) due to the reactant gas passing through thereactor tubes, and liquid is moving downwards in one or more liquidrecycle tubes (18). It was found that optimal heat transfer may beachieved by using a reactor that comprises liquid recycle tubes.

The reactor may comprise liquid recycle tubes of a different size thanthe reactor tubes: they may have a different inner diameter and/or adifferent length. Alternatively, the liquid recycle tubes may have thesame size as the reactor tubes. In that case, one may choose to fillmost tubes with catalyst and leave some tubes empty, i.e. use most tubesas reactor tubes and some tubes as liquid recycle tubes, before usingthe reactor. Reactant gas is preferably not fed to a liquid recycletube.

In case a tube which can be used as reactor tube is not filled withcatalyst in order to use this tube as liquid recycle tube, reactant gasis not fed to this liquid recycle tube. In such a case it may thus benecessary to close an outlet of the gas distribution system if this ispresent underneath or in the tube.

In one embodiment, the reactor comprises one or more liquid recycletubes which is/are situated outside the reactor shell. Such a liquidrecycle tube passes through the reactor shell at two differentlocations. A liquid recycle tube (18) situated outside the reactor shellmay extend through the reactor shell (2) above and below the coolantchamber (6) to enable fluid communication between the space (13) abovethe coolant chamber (6) and the space (15) below the coolant chamber(6). This allows a flow of liquid down the liquid recycle tube(s)outside the reactor shell during use of the reactor.

In a preferred embodiment, the reactor comprises a top outlet 5. In thatcase non-reacted gas and optionally gaseous product may leave thereactor via top outlet 5. If present, one or more top outlets 5preferably are situated above the coolant chamber, and may be situatedthrough the substantially vertical reactor shell above the coolantchamber and/or may be situated through the dome at the top of thereactor. The top outlet preferably comprises a nozzle.

In a preferred embodiment, the reactor comprises a top outlet throughthe dome at the top of the reactor and a gas-liquid separator, e.g. ademister or a cyclone, in the reactor underneath the top outlet. Agas-liquid separator may be used to limit the amount of material thatleaves the reactor through the top outlet, and increases the amount ofmaterial that leaves the reactor via a product outlet.

The reactor of the present invention is especially suitable for carryingout a Fischer-Tropsch process. When in use as Fischer-Tropsch reactor, areactor according to the present invention enables fluid communicationof syngas and fluid hydrocarbons between the space (15) below thecoolant chamber (6) and the space (13) above the coolant chamber (6)through the at least two reactor tubes (9) that extend through thecoolant chamber (6).

When used as Fischer-Tropsch reactor, the syngas is converted tohydrocarbons. The conversion products may be in the liquid phase, orpartial liquid and partial gas phase under reactor operating conditions.

During normal operation, the reactor tubes are filled with liquidproduct and the reactant gas is bubbled through the liquid product. Thisway optimal heat transfer from the catalyst to the coolant chamber isobtained via the liquid product. Also good transfer of reactants to thecatalyst structures may be achieved in this way. During normal operationas a Fischer Tropsch reactor, the reactor tubes are filled with liquidhydrocarbons and the syngas is bubbled through the liquid hydrocarbons.This way optimal heat transfer from the catalyst to the coolant chamberis obtained via the liquid hydrocarbons.

Coolant is preferably supplied to the coolant chamber via one or moreinlets at the lower side of the coolant chamber, and preferably leavesthe coolant chamber via one or more outlets at the upper side of thecoolant chamber. A very suitable coolant is water and/or steam. Boilingwater may be circulated through a natural circulation thermosyphonsystem with a steam drum. Alternatively, boiling hydrocarbons such askerosene may be used as coolant.

A reactor according to the present invention comprises a highly porouscatalyst. The catalyst has a size of at least 1 mm. Catalysts having asize of at least 1 mm are defined as catalyst having a longest internalstraight length of at least 1 mm. When of sufficient size, the highlyporous catalyst can be fixed in a reactor tube.

The catalyst preferably comprises a porous body and a catalyst material.The catalyst is also referred to as catalyst body. The porous body actsas support for the catalyst material. The catalyst material comprises acarrier and a catalytically active component or precursor therefor. Aprecursor of a catalytically active component can be made catalyticallyactive by subjecting it to hydrogen or a hydrogen containing gas.

A catalyst, or catalyst body, is defined for this specification as abody that either is catalytically active, or that can be madecatalytically active by subjecting it to hydrogen or a hydrogencontaining gas. For example, metallic cobalt is catalytically active ina Fischer-Tropsch reaction. In case the catalyst, or catalyst body,comprises a cobalt compound, the cobalt compound can be converted tometallic cobalt by subjecting it to hydrogen or a hydrogen containinggas. Subjection to hydrogen or a hydrogen containing gas is sometimesreferred to as reduction or activation.

When a catalyst is referred to as comprising a certain amount ofcatalytically active metal, reference is made to the amount of metalatoms in the catalyst which are catalytically active when in metallicform. A catalyst comprising a cobalt compound, for example, is thusconsidered as a catalyst having a certain amount of catalytically activecobalt atoms. A catalyst thus comprises a certain amount ofcatalytically active metal, regardless of its oxidation state.

The porous bodies may be of regular or irregular shapes, or a mixturethereof. Such include cylinders, cubes, spheres, ovoids, and othershaped polygons.

In a preferred embodiment the porous bodies have a form or shapeselected from the group consisting of gauze, honeycomb, monolith,sponge, foam, mesh, webbing, foil construct and woven mat form, or anycombination of these.

The porous bodies may be a combination of forms such as those listedabove. For example, the porous bodies may be made up of honeycomb shapedmaterial and have a circular outer shape. Another example is a cylindermade from woven mat.

The porous bodies may be made from any inert material capable ofwithstanding conditions within the reactor. The porous bodies may bemade from refractory oxides, for example titania, silica, alumina. Theporous bodies are preferably made from metals, for example stainlesssteel, iron or copper.

The porosity within the porous bodies, i.e. the internal voidage of theporous bodies before application of the catalyst material on the porousbodies, is within the range of between 50 and 98 volume %; preferablythe internal voidage is less than 95 volume %; preferably the internalvoidage is more than 60 volume %, more preferably more than 70 volume %,even more preferably more than 80 volume %, and most preferably morethan 90 volume %, calculated on the circumferential volume of the porousbodies.

The porosity of the catalyst, or catalyst body, i.e. including thecatalyst material and the porous body, is at least 50 volume % and ispreferably at least 65 volume %, more preferably around 85 volume %,calculated on the circumferential volume of the catalyst body.

The external voidage of the catalysts, or catalyst bodies, i.e.including the catalyst material and the porous bodies, in situ in areactor tube is in the range of between 0 and 60 volume %, calculated onthe reactor tube volume outwith the circumferential volumes of thecatalysts, or catalyst bodies, in the reactor tube.

In other words, a reactor tube may be completely filled with one or moreporous catalysts (catalyst bodies). In that case, the external voidagein situ in the reactor tube is 0 volume %, and all reactant gas andliquid product will pass through the porous structure of the catalystbodies. Alternatively, there may be space around the circumferentialvolumes of the catalyst bodies in situ in a reactor tube. In that case,the external voidage in situ in the reactor tube may be up to 60 volume%, and reactant gas and liquid product will pass through the porousstructure of the catalyst bodies and around the circumferential volumesof the catalyst bodies.

For example, in the case of a donut-shaped porous catalyst body made outof metal wires covered with catalyst material, the circumferentialvolume will not include the inner hole of the donut shape. In the caseof irregularly stacked donut-shaped catalyst bodies, reactant gas andliquid product will pass through the porous structure of the catalystbodies and around the circumferential volumes of the catalyst bodies.When passing around the circumferential volume of a catalyst body,fluids may pass the catalyst body at all sides, including through theinner hole of the donut-shaped catalyst body.

The porosity of the catalyst bodies, in other words the open volumeswithin the catalyst bodies, must be sufficient to facilitate efficientthrough-flow of reactants, while at the same time the specific surfacearea of each catalyst body should be as large as possible to increaseexposure of reactants to the catalyst material.

Suitable porous bodies on which the catalyst material can be applied,can be prepared in-house or obtained commercially. An example of aproducer of suitable porous bodies is the Fraunhofer-Institute forManufacturing and

Advanced Materials in Dresden, Germany. The Fraunhofer-Instituteadvertises and sells, for example, melt extracted metallic fibres, andhighly porous fibre structures that can be cylindrically or sphericallyshaped. Another example of a producer of suitable porous bodies isRhodius. Rhodius advertises and sells, for example, knitted wire meshesof various shapes, with various thicknesses and with various densities.Another example of a producer of suitable porous bodies is Fibretech.

The catalyst material may be applied to the porous bodies. Preferably athin layer of catalyst material is applied to the porous bodies.

The catalyst material layer is preferably sufficiently thin to avoiddiffusional mass transport limitations (decrease of CO and/or hydrogenpartial pressure and/or unfavorable change of the hydrogen/carbonmonoxide-ratio within the catalyst layer) of the syngas componentswithin the catalyst material layer. The thickness of the catalystmaterial layer is preferably increased up to the onset of mass transportlimitation. There is no upper limit to the thickness of the catalystmaterial layer onto the porous bodies other than the remaining voidageafter application of the catalyst material on the porous body forhydrodynamic reasons.

It is preferred that the catalyst material fraction of the catalystbodies is at least about 1% by volume and preferably greater than about4% by volume (with reference to the volume of the catalyst bodies), witha preferred maximum of 25% by volume.

Preferably the catalyst material is applied as a layer to the porousbodies, typically in a thickness of from about 1 to about 300 micronsand preferably from about 5 to about 200 microns.

General methods of preparing catalyst or materials are known in the art,see for example U.S. Pat. No. 4,409,131, U.S. Pat. No. 5,783,607, U.S.Pat. No. 5,502,019, WO 0176734, CA 1166655, U.S. Pat. No. 5,863,856 andU.S. Pat. No. 5,783,604. These include preparation by co-precipitationand impregnation. Such processes could also include sudden temperaturechange.

The catalyst material may comprise one or more metals or metal oxides aspromoters, more particularly one or more d-metals or d-metal oxides.

Preferably the catalyst is a Fischer-Tropsch catalyst. Fischer-Tropschcatalysts are known in the art, and typically include a Group 8-10 metalcomponent, preferably cobalt, iron and/or ruthenium, more preferablycobalt.

References to “Groups” and the Periodic Table as used herein relate tothe new IUPAC version of the

Periodic Table of Elements such as that described in the 87^(th) Editionof the Handbook of Chemistry and Physics (CRC Press).

Suitable metal oxide promoters may be selected from Groups 2-7 of thePeriodic Table of Elements, or the actinides and lanthanides. Inparticular, oxides of magnesium, calcium, strontium, barium, scandium,yttrium, lanthanum, cerium, titanium, zirconium, hafnium, thorium,uranium, vanadium, chromium and manganese are most suitable promoters.

Suitable metal promoters may be selected from Groups 7-10 of thePeriodic Table. Manganese, iron, rhenium and Group 8-10 noble metals areparticularly suitable, with platinum and palladium being especiallypreferred.

Any promoter(s) is typically present in an amount of from 0.1 to 60parts by weight per 100 parts by weight of a carrier. It will however beappreciated that the optimum amount of promoter(s) may vary for therespective elements which act as promoter(s).

Typically the catalyst material comprises a carrier material such as aporous inorganic oxide, preferably alumina, silica, titania, zirconia ormixtures thereof. The most preferred carrier material is titania. Thecarrier could be added onto the porous bodies prior to addition of thecatalytically active metal, for example by impregnation. Additionally oralternatively, the catalytically active metal and carrier material couldbe admixed and then added to the porous bodies. For example, a powderform of the catalyst material could be formed into a slurry, and thenspray coated onto the porous bodies.

A suitable catalyst comprises cobalt as the catalytically active metaland zirconium as a promoter. Another suitable catalyst comprises cobaltas the catalytically active metal and manganese and/or vanadium as apromoter.

In one embodiment, the reactor of the present invention comprises porousbodies of which more than 95 weight % (wt %), more preferably more than99 wt %, most preferably more than 99.9 wt %, has a size in the range ofbetween 1 mm to 50 mm, preferably 1 mm to 30 mm, calculated on the totalweight of the porous bodies in the reactor.

Catalyst bodies comprising porous bodies with a minimum size of 1 mm anda maximum size of up to 50 mm may be fixed within a reactor tube.Alternatively, they may be movable within a reactor tube so as to seekthe most even catalytic transfer and heat transfer, but without beingfixed within the reactor tube. With catalyst retainers it can be ensuredthat movable catalyst bodies stay within the reactor tube.

In one embodiment, the reactor of the present invention comprises largecatalyst bodies, i.e. larger than 50 mm, for example up to 500 mm, evenup to 2m.

Preferably the reactor of the present invention comprises porous bodiesof which more than 95 weight % (wt %), more preferably more than 99 wt%, most preferably more than 99.9 wt %, has a size in the range ofbetween 50 mm to 2 m, preferably 50 cm to 1 m, calculated on the totalweight of the porous bodies in the reactor. Catalyst bodies of more than50 mm may be immobilized within a reactor tube.

In a preferred embodiment, a reactor tube in a reactor according to thepresent invention comprises a catalyst retainer in the top and/or in thebottom of the reactor tube. Most preferably the reactor tubes in thereactor comprise both a catalyst retainer in the top and a catalystretainer in the bottom. A catalyst retainer allows gas and liquid topass through, but which does not allow catalyst bodies to go through. Anexample of a suitable catalyst retainer is a catalyst retainer made ofgauze with a sufficient mesh size. A catalyst retainer may be placed atan opening of a catalyst tube, and is preferably placed at the inside ofa catalyst tube.

In one embodiment, a reactor tube in a reactor according to the presentinvention may be filled with porous catalyst bodies in a stacked way. Inone embodiment, a reactor tube in a reactor according to the presentinvention may be filled with porous catalyst bodies to form a gradient.

Over the length of a reactor tube several properties may be varied. Forexample, the internal voidage of the catalyst bodies at the top of areactor tube may be lower than at the bottom. For example, the externalvoidage of the catalyst bodies at the top of a reactor tube may besmaller than at the bottom. For example, the amount of catalyst materialon the porous bodies may be larger at the top of the reactor tube thanat the bottom. The amount of catalytically active material in thecatalyst material on the porous bodies may be lager at the top of thereactor tube than at the bottom. The catalyst bodies at the top of thereactor tube may comprise a different catalytically active metal thanthe catalyst bodies at the bottom. The catalyst bodies at the top of thereactor tube may have a different shape as compared to the catalystbodies at the bottom of the tube.

In one embodiment, reactor tubes may be filled with catalyst bodies in astacked way, for example by loading two to four layers on top of eachother, whereby each layer has a different catalytic activity. In such acase each layer placed on top of another layer may have a higherintrinsic catalytic activity than the layer underneath. In a reactoraccording to the invention, the reactor thus may comprise one or morereactor tubes in which one or more layers of catalyst bodies in the topof the reactor tube has/have a higher intrinsic activity than one ormore layers of catalyst bodies in the bottom of the reactor tube.

The invention extends to the use of a reactor according to the presentinvention as a Fischer Tropsch reactor.

The invention further extends to a process for performing a FischerTropsch reaction comprising the steps:

-   -   providing syngas to a reactor according to the invention    -   removing Fischer Tropsch product from the reactor.

The Fischer-Tropsch reaction is preferably carried out at a temperaturein the range from 125 to 400° C., more preferably 175 to 300° C., mostpreferably 200 to 260° C. The pressure preferably ranges from 5 to 150bar, more preferably from 20 to 80 bar. The gaseous hourly spacevelocity may vary within wide ranges and is typically in the range from500 to 10000 Nl/l/h, preferably in the range from 1500 to 4000 Nl/l/h.The hydrogen to CO ratio of the feed as it is fed to the catalyst bedgenerally is in the range of 0.5:1 to 2:1.

Products of the Fischer-Tropsch synthesis may range from methane toheavy hydrocarbons. Preferably, the production of methane is minimisedand a substantial portion of the hydrocarbons produced have a carbonchain length of a least 5 carbon atoms. Preferably, the amount of C5+hydrocarbons is at least 60% by weight of the total product, morepreferably, at least 70% by weight, even more preferably, at least 80%by weight, most preferably at least 85% by weight. The CO conversion ofthe overall process is preferably at least 50%.

The shape, size and configuration of the reactor tubes and theirarrangement within a reactor are governed primarily by factors such asthe capacity, operating conditions and cooling requirements of thereactor. The reactor tubes may have any cross-section which provides forefficient packing of the catalyst within a reactor, for example, thereactor tubes may be of circular, square, triangular, rectangular,trapezoidal (especially covering three equilateral triangles) orhexagonal cross-section. A reactor tube having a circular cross-sectionis advantageous in terms of ease of manufacture, mechanical stability,and in providing uniform heat transfer.

The invention will now be explained in more detail with reference to thedrawing, which shows an example of a reactor according to the invention.

FIG. 1 is a vertical cross-section of a reactor according to the presentinvention; the catalyst in the reactor tubes is not shown.

FIG. 1 shows a reactor 1 for carrying out an exothermic process, such asa Fischer-Tropsch process, comprising a reactor shell 2, a reactantinlet 3, a product outlet 4, a top outlet 5, a coolant chamber 6comprising an inlet 7 and outlet 8 for a coolant, and reactor tubes 9.The reactor 1 further comprises a gas distribution system 11 below thecoolant chamber 6. The space below the coolant chamber 6 is indicated inFIG. 1 with number 15.

Parallel plates 16 and 17 separate the coolant chamber 6 from the space15 below the coolant chamber 6 and the space 13 above the coolantchamber 6.

During operation, syngas is fed through the inlet 3 to the gasdistribution system 11 and into reactor tubes 9 which comprise thecatalyst. As indicated in FIG. 1, the gas distribution system 11 passesgas into the reactor tubes 9 via distribution system outlets that are,in this case, placed inside each reactor tube.

The gaseous reactants pass through the reactor tubes 9, as indicated inFIG. 1 with arrow 10.

Liquid recycle will take place via liquid recycle tube 18. As indicatedwith the arrow in liquid recycle tube 18, liquid will flow down tube 18.

The upper part of the reactor 1 comprises a dome 12 having an innerdiameter equal to that of the main cylindrical section of the reactor 1.The space above the coolant chamber is indicated in FIG. 1 with number13.

In the space 13 above the coolant chamber 6 the product may rise to acertain level. In FIG. 1 the liquid level 14 of the product isindicated. Offgas may pass through the space 13 above the coolantchamber 6 to the top outlet 5. Liquid product is discharged via outlet 4below the coolant chamber 6 on the basis of level control (not shown)above the coolant chamber 6.

During operation, coolant, typically water and/or steam, is fed throughthe inlet 7 to the coolant chamber 6. There, the coolant is heated anddischarged via the outlet 8. Heat is transferred from the catalyst inthe reactor tubes 9 to the coolant in coolant chamber 6.

The invention is not limited to the embodiment described above, whichcan be varied in several ways within the scope of the claims. Forinstance, more than one coolant chamber may be used.

In a further example, the reactor according to the present invention canbe used for other exothermic processes including hydrogenation,hydroformylation, alkanol synthesis, the preparation of aromaticurethanes using carbon monoxide, Kalbel-Engelhard synthesis, andpolyolefin synthesis.

1. A reactor for carrying out an exothermic process comprising a reactorshell, inlets for introducing reactants and coolant into the reactorshell, outlets for removing product and coolant from the reactor shell,at least two reactor tubes, a coolant chamber, and a gas distributionsystem below the coolant chamber, whereby at least two reactor tubesextend through the coolant chamber to enable fluid communication betweenthe space below the coolant chamber and the space above the coolantchamber, said reactor comprising one or more highly porous catalysts,said catalyst(s) having a size of at least 1 mm and comprising a porousbody and a catalyst material, whereby the porous body has a porositywithin the range of between 50 and 98 volume %.
 2. A reactor accordingto claim 1, additionally comprising a top outlet.
 3. A reactor accordingto claim 1, additionally comprising at least two substantially parallelplates which separate the coolant chamber from the space below thecoolant chamber and the space above the coolant chamber.
 4. A reactoraccording to claim 1, additionally comprising one or more liquid recycletubes.
 5. A reactor according to claim 1, additionally comprisingcatalyst retainers at the top and the bottom of reactor tubes.
 6. Areactor according to claim 1, wherein the porous body has a form orshape selected from the group consisting of gauze, honeycomb, monolith,sponge, mesh, webbing, foil construct and woven mat form, or anycombination of these.
 7. A reactor according to claim 1, wherein theporous body is made from a metal.
 8. A reactor according to claim 1,wherein the porosity of the catalyst(s) is at least 50 volume %,calculated on the circumferential volume of the catalyst(s), and whereinthe external voidage of the catalyst(s) in situ in one or more reactortubes is in the range of between 0 and 60 volume %, calculated on thereactor tube volume outwith the circumferential volume(s) of thecatalyst(s) in the reactor tube.
 9. A reactor according to claim 1,wherein the reactor comprises one or more reactor tubes in which one ormore layers of catalysts in the top of the reactor tube has/have ahigher intrinsic activity than one or more layers of catalysts in thebottom of the reactor tube.
 10. A process for performing a FischerTropsch reaction comprising the following steps: providing syngas to areactor according to claim 1; removing Fischer Tropsch product from thereactor.